Keep app open when "Save as" is cancelled on close

[niksedk]

Problem

Reported by a user: closing a project with unsaved changes, choosing Yes to save, then cancelling the "Save as" dialog closed the app anyway — losing the work. The expected behaviour is to cancel the close (stay open).

Root cause

MainViewModel.OnClosing passed this to PromptSaveChanges:

async () => { await SaveSubtitle(); return true; }

It awaited the save but discarded SaveSubtitle()'s return value and always returned true. SaveSubtitle() → SaveSubtitleAs() correctly returns false when the file picker is cancelled, but that false never reached PromptSaveChanges, so the close proceeded as if the save had succeeded.

Fix

Propagate the real result: () => SaveSubtitle(). Now a cancelled "Save as" returns false → PromptSaveChanges returns false → OnClosing returns with e.Cancel still set, so the window stays open.

Fixed the identical lambda in the dead OnWindowClosing handler too (never subscribed, but fixed for consistency so it can't become a future trap). The other three PromptSaveChanges call sites already passed SaveCurrentSubtitle, which returns false on cancel, so they were already correct.

Testing

Verified manually in a local Debug build:

• Unsaved changes → close → Yes → cancel "Save as" → app stays open ✅
• Yes → save successfully → app closes ✅
• No → closes without saving ✅
• Cancel at the first prompt → stays open ✅

🤖 Generated with Claude Code